Stabilization of gasoline



Sept. 10, 1935. J, K. ROBERTS ET AL I STABILIZATION OF GASOLINE Filed Au 1, 1951 QKJYQZLZJ;

conditions of pressure and temperature.

Patented Sept. 10, 1935 UNITED STATES PATENT OFFECE STABILIZATION 0F GASOLINE Indiana Application August 1, 1931, Serial No. 554,534

1 Claim.

This invention relates to the stabilization of light hydrocarbon oils, and particularly to the stabilization of low-boiling oils derived from higher boiling hydrocarbon oils under cracking The invention will be more fully understood by reference to the following description in conjunction with the accompanying drawing which is an elevational view, somewhat diagrammatic in character, of apparatus suitable for carrying out the process of the invention.

Referring to the drawing, the numeral 5 indicates a fractionating column which receives low boiling vapor products through a line 6 leading from a cracking process wherein higher boiling hydrocarbon oils are subjected to cracking. The vapors supplied to column 5 may comprise all vapor products given off by the oil undergoing cracking and may, under such conditions, contain some constituents of higher boiling point than those desired in the finished stabilized product, or the vapors fed to column 5 through line 6 may be vapors from which a substantial portion of the heavier constituents have been separated; for example, the vapors may have been passed through a suitable dephlegmator wherein a substantial portion of such heavier constituents are condensed out before they are passed to column 5. The column 5 is provided with a plurality of spaced fractionating elements (not shown) of any suitable type, for example, bubble-cap plates, screen plates, or ring and disk plates. The heated vapors discharged into column 5 are subjected to fractionation to remove therefrom, as condensate, the higher boiling constituents undesired in the final distillate product, such condensate being withdrawn from the lower end of the column through a valved line I. The necessary cooling for fractionation may be effected by the introduction of a relatively cool fiuid into the upper portion of the column through a valved line 8 and/ or a cool fiuid may be passed through a coil 9 mounted in the upper portion to effect condensation of a portion of the vapors which condensate functions as a reflux cooling medium.

The fractionated vapors, substantially free of heavy undesired constituents, are withdrawn from the top of column 5 through line it! and pass to a heat exchanger ll wherein they give up a substantial portion of their heat to oil passed in indirect heat exchange therethrough, as hereinafter set forth. The cooled vapors and any condensate are passed from the other end of heat exchanger H througha line [2 and into a separator-drum l3.

It is preferred to cool the vapors, before passing them to drum 3, to a point at which substantially all constituents thereof, desired in the 5 final product, are condensed. If the vapors are not sufficiently cooled in the heat exchanger ll, additional cooling may be eifected by means of a cooling coil Ml provided in line l2.

The condensed desired constituents and the gases and uncondensed vapors of excessively volatile constituents undesired in the final product, separate within the drum IS, the gases and uncond nsed vapors being withdrawn through a valved line l5 and discharged from the system, and the condensate being withdrawn through line it and passed to the heatexchanger II. The condensate is substantially heated within exchanger H by the already described hot vapors flowing thereto from column 5, and is withdrawn 9 through line H and passed to a stabilizing column i8. The column I8 is maintained under a substantial superatmospheric pressure, preferably in excess of lbs., and is provided internally with a plurality of spaced elements (not shown) for 25 effecting intimate contact of vapors and liquids therein, for example, fractionating elements of a type similar to those employed in column 5, may be employed therein.

The heated oil discharged into the column [8 30 is subjected to rectification therein to remove therefrom substantially all of the excessively volatile constituents undesired in the final distillate product. The oil is introducedthrough line H into the column It at such a temperature 35 that a portion of it separates as vapor within the column $8, the vaporized portion consisting in part of the undesired excessively volatile constituents and in part of lower boiling constituents desired in the final product. The vapors ascend 40 through the column l8, and are fractionated therein, the uncondensed vapors passing out through a valved vapor line is to a condenser 29 wherein a portion of the vapors is condensed for refiux. The condensate together with the un- 45 condensed excessively volatile vapors or gases is passed from condenser 25 to a separator 2| wherein the condensate and gases or vapors are separated, the latter being withdrawn therefrom, and from the system, through a valved line 22. 50 The separated condensate is passed from the separator 2! through a line 23 to a pump 24 by which it is forced through a line 25 into the upper portion of the column 18 to serve as a downwardly flowing reflux cooling medium therein.

The unvaporized portion, from which substantially all of the undesired excessively volatile constituents have been removed, is withdrawn from the bottom of column 58, and from the system, through a valved line 26. The unvaporized portion may be passed from line 26 through a cooler 27. It is preferred to operate the column l8 so as to maintain a substantial body of such liquid portion in the bottom of the column 58 and supply heat to such liquid body to effect reboiling thereof. This reboiling may be accomplished by passing steam or other hot fluid through a coil 28 provided therein.

In a specific operation, vapors comprising constituents within the gasoline range of boiling points and containing some undesired excessively volatile products and some undesired higher boiling products, were supplied to column 5 through line 6. The column 5 was maintained under 200 lbs. pressure and sufiicient cooling was effected therein to maintain a temperature of about 420 F., at the vapor outlet thereof. The condensed products were withdrawn from the bottom of the column through line i and consisted of substantially all the undesired higher boiling constituents of the original vapors. The vapors withdrawn from column 5 were cooled by the condensate from separator E3 to about 290 F., the vapors fiowing through the exchanger l i countercurrent to the flow of condensate therethrough. Additional cooling of products from column 5 was eifected by means of the coil i i so that they were cooled to about 85 before they were introduced into the separator E3. The condensate withdrawn from separator l 3 was heated to about 350 F. in the heat exchanger 5! by the already described vapors passing therethrough from column 5. The column E8 was maintained under substantially the same pressure as that in the column 5 less, of course, any differential required to effect a substantial flow through the system. Under such pressure conditions, the top of the column 58 was maintained at about 110 F., and the bottom was maintained at about 370 F. The finished product withdrawn through line 25 constituted a stabilized pressure distillate substantially free of undesired excessively volatile, and undesired higher boiling constituents. The uncondensed vapors or gases withdrawn from separators l3 and 2:, through lines l5 and 22, respectively, consisted of substantially all the excessively volatile constituents undesired in the final stabilized distillate product, and contained substantially none of the most volatile constituents desired in the final distillate product.

In accordance with the present invention, the heat and pressure of vapors from a pressure cracking operation are employed for the substantially complete stabilization of such vapors.

While the above description indicates that we may employ substantially the same pressure in our stabilization process and apparatus as that employed in the fractionator or dephlegmator of the cracking system from which our process and apparatus receives the stock to be treated, it is to be understood that we may employ higher or lower pressures in all, or any part of our sys tem. For example, a pump (not shown) may be interposed in line I5 whereby the column 18 may be operated at a pressure higher than that in column 5, or the cracking system, and/or one or more suitable pressure reducing valves may be employed in the system to reduce the pressure in any one or more of the stages thereof. It will be seen that the amount of heating of condensate from separator i3 and/or cooling of vapor from column 5 may be varied by employing a heat-exchanger which provides for a longer or shorter counter-current flow, therethrough, of such products. Also, it will be understood that some extraneous heat may be employed in various parts of the system in addition to that furnished by the vapor from the pressure distillation process. For example, the lower portion of column 8 may be supplied with additional heat to effect reboiling of liquid condensate within the column l8.

It is to be understood that the specific details of apparatus and method hereinbefore set forth are for the purpose of illustration, and are not intended to be regarded as limitations upon the scope of the invention, except as contained in the following claim.

We claim:

The method of stabilizing hot vapors which comprises partially cooling said hot vapors in a first cooling zone to effect condensation and. separation of substantially all of the constituents heavier than those desired in the final distillate product, removing the remaining vapors and passing them first in indirect heat exchange with a distillate stock, to partially condense vapors and heat said distillate stock, then in indirect heat exchange with another cooling medium to cause the final desired degree of com densation oi the vapors, whereby substantially all of the constituents thereof desired in the final product are condensed, with some undesired constituents, collecting resulting condensate and removing incondensible gases therefrom, passing condensate so obtained in indirect heat exchange with said hot vapors, as said distillate stock, whereby said hot vapors are initially cooled and said condensate is heated, introducing resulting heated condensate into an intermediate point in a stabilizing column under substantially superatmospheric pressure wherein substantially all of the remaining undesired excessively volatile constituents are separated as vapors from said desired constituents as liquids, removing said undesired excessively volatile constituents from the top of said column, withdrawing the stabilized product from the base of said column and applying additional heat from an external source to the base of said column.

JOSEPH K. ROBERTS. GEORGE W. WATTS. 

